In internal combustion engines, it is common to utilize a carburetor that includes a choke. The choke functions when the engine is cold to provide a rich mixture. As the engine begins to run and the vacuum increases, a choke pull-off is provided that functions under the action of manifold vacuum to return the choke to the open position so that the fuel air mixture is at a normal less rich mixture. A typical system of this type is shown in U. S. Pat. No. 3,773,023 which shows a diaphragm operated choke pull-off that also includes a check valve. Other typical systems are shown in U. S. Pat. Nos. 3,991,731 and 4,382,899. U. S. Pat. No. 3,991,731 describes a Choke Pull-Off assembly incorporating the following features: time delay valve, filter, purge air flow with filter, and a check ball.
One of the problems with such an arrangement is that any delay built into the Choke Pull-Off assembly is relatively constant at all temperatures. It may be desirable to provide a longer time delay at low temperatures (below 20.degree. F.) and a shorter time delay, or no delay, at moderate temperatures, (above 30.degree. F.).
Accordingly, among the objectives of the present invention are to provide a system wherein the choke pull-off action will be delayed whenever the temperature is below a predetermined value; and when the temperature is above the predetermined value, there will be no delay and the flow of vacuum to the choke pull-off will be instantaneous and unrestricted, while incorporating the desirable features described in U. S. Pat. No. 3,991,731.
In accordance with the invention, the temperature compensating vacuum delay valve comprises a housing having a first opening adapted to be connected to manifold vacuum and a second opening adapted to be connected to a choke pull-off assembly which functions to partially open the choke when a vacuum is applied to the choke pull-off assembly. The housing includes a valve disc, a seat, and means yieldingly urging the valve disc against said seat. A restrictor permits restricted flow between the one side of the valve disc and the other side of the valve disc when the valve disc is in sealing position and a bi-metallic disc is positioned in the housing between the first opening and the valve disc and is operable upon predetermined change of temperature to move the valve disc away from a seat and thereby permit unrestricted flow between the first opening and the second opening.